404 
MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
the opisthotics (op.), and the prootics (pro.) ; its fore edge is attached by the medium 
of a band of cartilage to the basisphenoid (bs.). 
The condyle, which is practically single, although morphologically double, has both 
this basal and the two lateral bones entering it. 
The foramen magnum is finished above by the lateral bones, or exoccipitals (eo.) ; they 
also send backwards from their upper edge an imbricating process to rest upon the “atlas.” 
The 9th, 10th, and 12th nerves (9, 10, 12) pierce these bones below; their front 
margin turns outward in such a manner as to clamp the hind part of the auditory 
mass, and they thus form a deep salcus on the inner face, the auditory mass swelling 
out in front of the out-turned exoccipitals (fig. 3, eo., op). 
The key-stone of the arch or superoccipital (so.) lies on their fore margin ; it is a 
transverse slab, with five sides : the foremost side is emarginate in a concave manner, 
finishing the rounded outline of the great upper fontanelle (fo.). 
This roof-slab just touches the opisthotic (fig. 6, o p.) ; is imbricated by the epiotics 
(ep.), and is joined to its own side plates (eo.) by synchondrosis. 
Here we behold a normal and primary condition, not seen in the hot-blooded 
“ Sauropsidan ” Bird — namely, the freedom of the occipital bones from all participation 
in lodging the labyrinthic canals of the ear ; they are confined to their own periotic 
region and bony centres. 
The great bones of the otic mass are three only, not five as in Osseous Fishes. For in 
the Snake the head is made into a terete wedge ; all snags, projections, buttresses, and 
the like are smoothed down. Thus there is no endoslceletal post-frontal (“ sphenotic ”), 
nor lateral ear-eave (i legmen ) over the horizontal canal, to be ossified by the “ pterotic.” 
These three bones are divided by a fine line of cartilage which is bifurcated above, so 
that it is triradiate (figs. 3, 4). 
The huge semicircular canals (a.sc., h.sc., p.sc.) have long ago so dominated the whole 
capsule as to force it into conformity with their arches and swelling ampullae ; the 
vestibule and cochlea are relatively small. 
Also the bony walls being merely the ossified cartilaginous capsule, with but little 
periosteal deposit, keep the very form, outside, of the elaborately ornate contents. 
The foremost of the three, the prootic (pro.), is equal in size to the other two ; and the 
opisthotic (op.) is the larger of these ; the smallest of the three, the epiotic (ep.) 
contains no ampulla ; the prootic has two, and the opisthotic one, of the pouches. 
The prootic bone encloses the ampullae of the anterior and of the horizontal canals ; 
it runs along their pipes, and reaches to the middle of the horizontal and to the last 
third of the anterior canal. 
Below, its anterior part rests upon the small alisphenoid, and behind that it runs down 
and rests equally upon the basisphenoid and basioccipital, wedging in between them. 
The prootic forms the back to the foramen for the third part of the trigeminal nerve, and 
encloses the passages of the 7th and Sth (figs. 3, 4 ; 5 3 , 7, 8) ; it ensheaths the fore face 
of the cochlear pouch, and forms the front margin of the fenestra ovalis (cl.,fi.o.). 
